The isolated rabbit retina will be used as a prototype of brain for 3 collaborative studies. The first study will used isotopically labelled amino acids to measure amino acid transport and protein synthesis and breakdown in order to determine what types of proteins are involved in the rapid turnover that has been previously described and to determine how this turnover is affected by function and by certain chemical variables. In the second study, we will measure the response of specific neuronal circuits in the retina to agents that potentiate or inhibit specific neurotransmitters in order to obtain information about the transmitters normally involved in these circuits. In the third, we will study the retina's response to, and recovery from, short periods of ischemia to elucidate the mechanisms of the ischemic insult and to identify what it is that determines irreversibility.